Phosphor screen comprising two kinds of particles, each having phosphor core and phosphor coating

ABSTRACT

An electron tube having a penetration-type luminescdnt screen which includes phosphor particles of two different types. A builtup particle of the first type is comprised of a core of a first phosphor, a coating of an inert electron-absorbing layer, and an overcoating thereon of a third phosphor. A builtup particle of the second type is comprised of a core of a second phosphor, a coating of an inert electron-absorbing layer, and an overcoating thereon of the third phosphor. At low operational voltages, the third phosphor (the overcoating) is excited to produce a colored emission to the viewer. At higher operational voltages, the first phosphor and the second phosphor (cores) of similar persistences are simultaneously excited to emit in different colors to produce a combined light of a white or off-white emission to the viewer. Thereby, the viewer may observe an information display in white or off-white and a related display in an easily distinguishable contrasting color such as red.

United States Patent Martin Robert Royce [72] Inventor Lancaster, Pa. [21 Appl. No. 880,865 [22] Filed Nov. 28, I969 [45] Patented Nov. 23, 1971 [73] Assignee RCA Corporation [54] PHOSPHOR SCREEN COMPRISING TWO KINDS OF PARTICLES, EACH HAVING PHOSPHOR CORE AND PHOSlPl-IOR COATING 2 Claims, 6 Drawing Figs.

[52] US. Cl 313/92 PH, 313/92 R [51] lnt.Cl ..H0lj 29/18, H0 1 j 3/20 [50] Field of Search 313/92 B, 70 C, 92

[56] References Cited UNITED STATES PATENTS 3,371,153 2/1968 Matzen 313/92X 3,517,243 6/1970 Jones 313/92 3,522,463 8/1970 Bishop ABSTRACT: An electron tube having a penetration-type luminescdnt screen which includes phosphor particles of two different types. A builtup particle of the first type is comprised of a core of a first phosphor, a coating of an inert electron-absorbing layer, and an overcoating thereon of a third phosphor. A builtup particle of the second type is comprised ofa core of a second phosphor, a coating of an inert electron-absorbing layer, and an overcoating thereon of the third phosphor.

At low operational voltages, the third phosphor (the overcoating) is excited to produce a colored emission to the viewer. At higher operational voltages, the first phosphor and the second phosphor (cores) of similar persistences are simultaneously excited to emit in different colors to produce a combined light of a white or off-white emission to the viewer. Thereby, the viewer may observe an information display in white or offwhite and a related display in an easily distinguishable contrastin g color such as red.

PATENTEDNHV 2 3.622.826

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INVENTOR Martin R. Royce AUOBNE) PHOSPIIOR SCREEN COMPRISING TWO KINDS OF PARTICLES. EACI'I HAVING PI-IOSPHOR CORE AND PI-IOSPI-IOR COATING BACKGROUND OF THE INVENTION The invention relates to a novel electron tube having a penetration-type luminescent screen which displays information in both white and a color depending on the applied voltages. Display tubes of this type may be used, for example, in computer data display terminals, military identification systems, stock market quotation displays, and so forth.

Some prior art multilayer penetration-type screens have been previously described, for example, in U.S. Pat. No. 3,204,143 to D. N. Pritchard. This patent describes color television picture tubes having penetration-type screens of both the extended layer type and the particle layer type known in the art as onion skin layers.

Another prior art penetration type screen is described in a U.S. Pat. application of A. E. Bishop filed July 15, I968, Ser. No. 744,887. This application describes an electron tube having a multicolor, dual-persistence screen. A screen structure of this type relies on each phosphor having a different persistence characteristic to permit viewers to distinguish information according to colors and persistence of each color.

It is desirable that high-speed graphic display cathode ray tubes provide a continuous display of information in a white or off-white color and a relating display of information in a contrasting color. A display using a red emission contrasting with a white or off-white emission is desirable to instantly permit identifying a portion of a message as belonging to one of two categories.

SUMMARY OF THE INVENTION The novel electron tube is comprised of an evacuated envelope, a luminescent screen therein, and means for exciting the screen with electrons. The screen is comprised of built up particles of at least two different types. Each of the built up particles of one type includes a base particle or core of a first phosphor which luminesces in one visual color. Each of the built up particles of the other type includes a base particle or core of a second phosphor which luminesces in another visual color. The first and second phosphors have approximately the same decay characteristics and, when simultaneously excited, the emissions add to produce a light mix output display which appears white or off-white to a viewer. Each of the cores of both particle types has an inert electron energy-absorbing coating and is overcoated with a third phosphor which when excited emits in still another color. The third phosphor may have approximately the same, a longer, or a shorter decay characteristic as the first and second phosphors.

The tube is operated at two voltage levels. At the low-voltage level, the third phosphor (the overcoating) is excited to produce a colored emission to the viewer. At the high-voltage level, the first and second phosphors (from the cores) are excited simultaneously to produce a white or off-white emission to the viewer. The use of a white emission in combination with a contrasting colored emission provides continuous viewing of two related displays of information. If the two emissions are red and white, for example, a continuous display of information can be viewed in white, and a related display of information can be viewed in red. Alternatively, a continuous display of information can be viewed in white and a display of information can be viewed only for special purposes in red, such as for a danger signal or for a variance from a prescribed program.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a longitudinal section of a novel cathode-ray tube incorporating the novel screen of the invention.

FIG. 2 is an enlarged broken-away section of the luminescent screen included in FIG. 1.

FIG. 3 is an idealized sectional view of the first type of built up phosphor particle used in the screen illustrated n FIGS. 1 and 2.

FIG. 4 is an idealized sectional view of the second type of built up phosphor particle used in the luminescent screen illustrated in FIGS. 1 and 2.

FIG. 5 is a graphical representation of the typical trace luminance characteristics of the white and red color displayed on the screen of the novel display tube illustrated in FIG. 1.

FIG. 6 is a typical color designation diagram illustrating how the emissions of the phosphors are chosen to obtain a specific red-to-white or off-white range of emission which can be viewed on the screen of the novel display tube shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a novel cathode-ray tube 10 comprised of an envelope 11 including a neck 12, a faceplate 13 and an interconnecting funnel 14. An electron gun 15 in the neck 12 is adapted to project a beam 16 of electrons toward the faceplate 13. The neck 12 is closed at one end with a stem structure 17 through which a plurality of lead-in wires 18 are sealed. Suitable operating potential is supplied to the electron gun 15 through the lead in wires 18. A conducting coating 19 is provided on the internal surface of the funnel 14 and serves as an accelerating electrode for the electron beam 16. A suitable high-voltage potential is supplied to the conducting coating 19 through a terminal means sealed through the funnel l4 and schematically represented by arrow 20. Means, such as a magnetic deflection yoke 21, are provided for deflecting the electron beam .16 to scan a raster over the faceplate 13.

A luminescent screen 22 is supported on the internal surface of the faceplate 13 in a position whereby the deflected electron beam 16 may excite the screen 22 to luminescence. FIG. 2 illustrates in more detail the luminescent screen 22 which is comprised of a single layer 23 of phosphor-coated phosphor particles. The layer 23 is characterized by having a thickness substantially greater than the size of the coated particles, thus resulting in a multiparticle thick layer 23 which is substantially free of perforations and voids. Because the particles are ordinarily small in size, the layer 23 is relatively thin. A light-reflective metallic layer 24 of, for example, aluminum, is supported on the phosphor layer 23.

The layer 23 is comprised of a mixture of two different types of built up phosphor particles. The first type of built up phosphor particle, illustrated in FIG. 3, includes a first core 25 of a medium-to-short-decay cathodoluminescent phosphor. The decay of luminescence is in the range of l millisecond to 1 micro second. The first core 25 may be, for example, a silveractivated zinc sulfide particle which exhibits a blue emission and a decay of about 35 microseconds. The first core 25 has a particle size in the range of 15 to 40 microns.

The first core 25 has an inert electron-absorbing coating 26 such as, for example, vermiculite, or a silica having the trade name Ludox, marked by E. I. du Pont de Nemours and Company, Wilmington, Del. The coating 26 may also be integral with the first core 25, such as is obtained by diffusing cobalt into a surface region of the first core 25 which by subsequent treatment renders it nonluminescent. The coating 26 is approximately 0.I to l.0-micron thick. The preferred thickness is approximately 0.5 micron.

The first core 25 with coating 26 has an overcoating 27 of a short-to-medium-decay cathodoluminescent phosphor. The overcoating 27 may be, for example, a red-emitting manganese activated zinc magnesium cadmium silicate, europiumactivated yttrium vanadate, or europium-activated yttrium oxysulfide. The overcoating 27 is approximately 0.1 to 1.0- micron thick and exhibits a decay of approximately 1 millisecond.

The second type of phosphor particle, illustrated in FIG. 4, includes a second core 28 of a medium-to-short-decay cathodoluminescent phosphor. The decay of luminescence of the second core 28 is in the range of l millisecond to l microsecond and approximately the same as that of the first core 25. The second core 28 may be, for example, a silver-activated zinc cadmium sulfide particle which exhibits a yellow emission and a decay of about 35 microseconds. The second core 28 also has an inert electron-absorbing coating 26 and an overcoating 27 of the same phosphor of the overcoating of the first particle.

The luminescence decay characteristics of the first and second cores 25 and 28 should be very similar since their emission output provides a white light display to the human eye. If one of the first and second cores 25 or 28 has a longer persistence, then a residual image of an undesired color (nonwhite) may result. It is desirable that the luminescence decay of the first and second phosphor cores be within the range of 25 to 75 microseconds. The preferred decay range is 50 to 60 microseconds.

The luminescence decay characteristic of the overcoating 27 may be approximately the same as that of the first and second cores 25 and 28. This will permit equal sequential scanning for both the overcoating and the cores and result in continuous image displays of both colors to the human eye. The luminescence decay characteristics of the overcoating 27 may also be longer or shorter than that of the cores 25 and 28.

The tube produces an electron beam 16 which may have electrons of different velocities. Means may be provided in the tube 10 for preventing rastersize distortion. Such means may take the form of eithera mesh 29 disposed tra'versely within the funnel 14 or other suitable means. Where the mesh 29 is used, it is connected to the conductive coating 19, and the tube 10 is operated according to post-acceleration principles. A separate lead-in means as indicated schematically by arrow 30 may be provided for supplying suitable electrical potentials to the metallic layer 24 for the purpose of obtaining post-acceleration operation of this if so desired. However, the mesh electrode 29 and the separated lead-in wire 30 may be omitted entirely.

The concept of the operation of the novel tube may be described by reference to FIGS. 3 and 4, which show idealized sectional views of the built-up particles of the two types. In the first type built-up particle (FIG. 3), an overcoating 27 covers an electron-absorbing coating 26 and a first core 25 of a first phosphor. In the second type particle, the same overcoating 27 covers an electron-absorbing coating 26 and a second core 28 of a second phosphor. The phosphors of the first and second cores 25 and 28 are chosen only to add in color emission and produce a white or off-white color to the human eye. Since the two types of built-up particles are mixed to form the screen layer 23, the first and second cores 25 and 28 are simultaneously excited by the high-voltage electrons producing a light mix output, and only a white or off-white color is observed by the human eye. Therefore, a signal from a computer having a high-speed scanning rate may be displayed in a continuous white or off-white pattern by the simultaneous emission from the first and second cores 25 and 28. A sta tionary or moving reference mark or pattern may also be displayed in a second color, such as red, by the emission from the overcoating 27 without creating persistent images that could be confused with or obscure the signals from the aforesaid source having a high frame rate.

In making the screen 22, the two types of built-up phosphor particles may be prepared together or separately. It is preferred to use a coating method described in U.S. Pat. NO. 3,275,466 to R.D.Kell. In one application of the Kell method, the first type of particle is prepared by soaking phosphor first cores 25 of the first type in a particle-absorbing liquid, such as an acidified gelatin solution. The soak is agitated to ensure particle liquid contact. The first cores 25 are then allowed to settle, and the excess liquid is poured off leaving an adsorbent film on the first cores 25. The film coated first cores 25 are then washed in water one or more times. Next, the inert electronabsorbing layer 26 is laid down on the first cores 25 by a similar soaking procedure. A suitable material such as submicron-size vermiculite particles dispersed in water is put in the soak along with the gelatin filmed first cores 25. The materials in the soak are agitated to coat the phosphor first cores 25 with an inert coating 26. The first cores 25 are then allowed to settle and the excess inert material is poured ofi'. The film-coated first cores 25 are then washed in water. Additional applications of absorbent film and inert electron-absorbing material may be laid down to increase the coating 26 thickness.

Another method of applying the inert layer is described in U.S. Pat. No. 3,294,569 to P. .l. Messineo et al. This patent describes a method of diffusing an integral inert layer of cobalt sulfide into the outer portion of the phosphor core.

When the inert electron-absorbing coating 26 is sufficiently thick, the phosphor overcoating 27 is applied. An absorbent film is applied to the coated particles as described above. The film-coated first cores 25 are soaked in a water suspension of submicron-size particles of the third phosphor. The first cores 25 are agitated in the suspension whereby the submicron particles of the overcoating 27 are deposited on and overcoat the first cores 25. The overcoated filmed first cores 25 are then decanted from the remaining suspension and washed with water. These latter steps may be repeated to increase the thickness of the phosphor overcoating 27 on the coated core 25. When the overcoating 27 is sufficiently thick, the particles are washed and stored in water.

After the final application of the third phosphor, the overcoating 27 may be given a final treatment to improve the adherence thereof. This may be done by washing the overcoated first cores 25 with a solution of formaldehyde, chrome alum, or potassium silicate.

The foregoing steps are repeated using core particles 28 of the second phosphor in place of core particles 25 of the first phosphor to prepare the built-up phosphor particles of the second type.

Quantities of the built-up particles of the first and second types are blended in the desired proportions by mixing to form an aqueous suspension. The suspension is then used to deposit the phosphor layer 23, as by a slurry coating process or by a settling process.

The layer 23 of built-up phosphor particles is filmed and a metallic layer of aluminum 24 applied, as by vapor deposition, in a manner known in the art. Then, the entire screen structure including the aluminum layer 24 is heated, whereby the volatile materials are removed.

Some specific combinations of commercially available phosphors which may be used to practice the invention are:

l. for the first cores 25: RCA-3 3z 20D 2. for the second cores 28: RCA-3 3-Z-250 3. for the overcoating 27: RCA-33Y-25 3A These phosphors are marketed by RCA Corporation, Harrison, N. J. The specific phosphor combination used in the screen structure 22 of the novel display tube is a proportion of about 37.6 grams of the first type particle and about grams of the second type particle. Approximately 6 to 7 grams of the third phosphor of the overcoating 27 are used with the 100 grams of the first core 25 or the second core 28 to make either the first or second type built-up particle.

In FIG. 5, the average brightness of the center of a single trace is related to the scan sweep speed for the novel display cathode-ray tube. FIG. 5 shows the relationship in brightness between the red and the white display and the scan rate. The scan is refreshed at 60 Hz. providing a red display at approximately ll kv. anode voltage and a white display at approximately 16 kv. anode voltage. The novel display cathode-ray tube is sequentially scanned for red and white over the complete tube display providing a continuous two-color display to a viewer.

FIG. 6 describes the range of red to white emission obtainable from preferred embodiment of the novel cathode-ray tube. The emission of the phosphor used for the first core 25 is shown by the point 29, the emission of the phosphor used for the second core 28 is shown by the point 30, and the emission of the phosphor used for the overcoating 27 is shown by the point 33. The tube produces data either in red at a dominant wavelength of 6070 angstroms, or in white which is similar to the CH5. Illuminant A" 37. The tube may also be operated to display any given color between the red emission 33 and the white or off-white emission 32, as described by the locus 34 of the mixture of the two colors, by control of applied anode voltage.

One method of selecting a particular red-to-white range of color emission is to first select the proportions of the first and second type built-up particle to determine the white emission by simultaneous excitation of the first and second cores and 28. The theoretical white-emission range obtainable from the first and second cores 25 and 28 is shown in FIG. 6 by the portion of the locus 31 of the mixture of the emissions in the white area. The white emission as used in this specification includes the white and off-white emissions described by the elliptical area labeled white" in FIG. 6. In the specific embodiment used in the novel cathode-ray display tube a proportion of about 37.6 grams of the first type particle and about 100 grams of the second type particle theoretically provides a white emission shown by the point 32 in FIG. 6.

After the white emission 32 is determined, the theoretical red-to-white emission is described by the locus 34 between the red emission 33 and the white emission 32. The theoretical white emission 32 is usually not obtained in the novel display tube since the high-voltage electrons in exciting the first and second cores 25 and 28 also slightly excite the overcoating 27. The slight emission from the overcoating produces an actual white emission 35 displaced from the theoretical white emission 32 toward the red. The extent of the displacement is affected by'the difference between the high and low voltages and the effectiveness of the inert coating 26. Since the simultaneous emission by the high-voltage beam also includes a small amount of emission from he overcoating 27, the theoretical white emission 32 can be outside the white area shown in FIG. 6. It is only necessary that the viewed white emission 35 be within the white area shown in FIG. 6.

Other ranges of red-to-white emissions can be obtained in the novel cathode-ray display tube. The selection of different proportions of the first and second type built-up particles will move the theoretical white along the locus 31 of possible whites within the white area shown in FIG. 6. The theoretical range of red to white occurs along the locus 34. The actual white 35 for each possible range of red to white will occur on the locus 34 of theoretical red to whites displaced by the amount of emission from the overcoating as approximately illustrated by the locus 36 of whites obtainable.

Although the locus 31 of theoretical whites occurs between the emission from the first core 25 (yellow) and the emission 29 from the second core 28 (blue), it can occur between any two phosphor color combinations that are displaced opposed over the white area of FIG. 6 such as, for example, phosphors having an orange emission and a cyan emission. The first and second phosphors used for the first and second cores 25 and 28 can also have a red and cyan emission. The colored emission from the overcoatings 27 can also be any contrasting color providing other color ranges such as blue-towhite and green-to-white by varying the third phosphor. A contrasting color as used in this specification is a saturated or near-saturated red, orange, blue or green color.

Iclaim:

1. An electron tube comprised of an evacuated envelope, a luminescent screen therein, and means for exciting said screen with electrons within said envelope, said screen being comprised of particles of at least two different types,

each of the particles of a first cathodo-luminescent type being comprised of a base particle of a first phosphor consisting of silver-activated zinc sulfide which luminesces with a persistence P in the range of 25 to 75 microseconds in a first color blue upon excitation with electrons, and inert electron-absorbing coating on said base particles, and an overcoating thereon of a third cathodo luminescent phosphor selected from the group consisting of a red-emitting manganese-activated zinc magnesium cadmium silicate europium activated yttrium vanadate, and euro ium-activated yttrium oxysulfide whlch lumlnesces W] a persistence P in the range of 25 to 75 microseconds in a third color red upon excitation with electrons,

each of the particles of a second type being comprised of a base particle of a second cathodo luminescent phosphor consisting of silver-activated zinc cadmium sulfide which luminesces with a persistence P in the range of 25 to 75 microseconds in a second color yellow upon excitation with electrons, an inert electron absorbing coating on said base particle, and an overcoating thereon of said third phosphor which luminesces with a persistence P in said third color upon excitation with electrons,

said persistences I and P being about equal,

and the simultaneous excitation of said first and second phosphors in said screen producing an emission that appears white of off-white to the viewer.

2. The tube defined in claim 1 wherein.

P is about 35 mircroseconds P is about 35 microseconds P is about 1 millisecond n w a Abstract,

Column 1,

Column 4,

Column 6,

Column 6,

(SEAL) Attest:

Patent No.

UNITED STATES PATENT OFFICE Dated November 23, 1971 Inventor(s) Martin Robert Royce lines 1 and 2 line line

line

line

Signed and It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as, shown below:

change "luminescdnt" to -luminescentafter "message" insert -or a given message-- after "with" cancel the-- cancel "cathodo-luminescent" after "first" add -cathodo1uminescent-- sealed this 13th day of June 1972.

EDWARD M.FLEI'CHER, JR. Attesting Officer ROBERT GOTTSCHALK Commissioner of Patents USCOMM-DC 60375-969 us GOVERNMENT PRINTING orrn: I969 o-aee-au 

2. The tube defined in claim 1 wherein. P1 is about 35 mircroseconds P2 is about 35 microseconds P3 is about 1 millisecond 